With the increase in communication demand, a high-speed transmission system based on the technology of Ethernet is standardized. In IEEE802.3ba (IEEE: The Institute of Electrical and Electronics Engineers, Inc.), 40 GBASE-R and 100 GBASE-R which are transmission technology of about 40 Gbps and about 100 Gbps are specified, respectively, for example.
On the other hand, also in ITU-T (International Telecommunication Union Telecommunication Standardization Sector), the high-speed transmission technology which is adapted to the above-mentioned standard is prescribed. ITU-T recommendation G.709 prescribes technology of the Optical Transport Network (OTN) of about 40 Gbps and about 100 Gbps. This technology enables the high speed transmission of not only a frame of SDH (Synchronous Digital Hierarchy) and SONET (Synchronous Optical NET) which mainly accommodate data a sound but also an Ethernet frame which mainly accommodates data.
When a transmission device receives an optical signal in which the high-speed transmission has been performed, the transmission device performs optoelectronic conversion on the optical signal, deserializes data on an electric signal obtained by the optoelectronic conversion, with a SerDes (Serializer/Deserializer) function, thereby generating a plurality of electric signals. For example, the electrical signal of about 100 Gbps is converted into the electrical signals of about 10 Gbps×10 lanes. The electrical signal of about 40 Gbps is converted into the electrical signals of about 10 Gbps×4 lanes. The conversion process is performed in order to reduce the transmission speed of data to the degree that a logic circuit in the device can electrically process the data.
The transmission characteristics of the above-mentioned electric signals are determined according to setting values of circuits that control analog electrical characteristics in SerDes function units of a transmitting end (Tx) and a receiving end (Rx). With respect to adjustment of the setting values, a patent document 1 (see Japanese Laid-Open Patent Publication No. 2006-60808) discloses technology that transmits and receives data having a given pattern, and sets a preemphasis control value so that a transmission error of the data becomes minimum, for example. A patent document 2 (see International Publication Pamphlet No. WO 2009/013790) discloses technology that selects a plurality of combinations including an amplitude, an emphasis characteristic and so on of a signal on a transmission channel, and sets the amplitude, the emphasis characteristic and so on included in a combination extracted based on an error rate of the transmission channel.